1. Field of the Invention
The present invention relates to a transportation vehicle system, in particular, to a system of transportation vehicles that travel using secondary batteries.
2. Description of the Related Art
Rechargeable secondary batteries are mounted on overhead traveling vehicles, rail guided vehicles, automated transportation vehicles or the like as the power supplies on the vehicles. In this regard, Patent Publication 1 (JPH05-207611A) proposes to provide a battery replacement machine for replacing batteries of the overhead traveling vehicles. For the transportation vehicle system using the second batteries, a system that controls reliably the state of charge (remaining capacity) of the battery and minimizes the loss time due to charging of the transportation vehicles is required.